The development of the Category 6 standard (ANSI/TIA/EIA-568-B.2-1) and its subsequent wide acceptance by the telecommunications industry has raised the transmission requirements for electrical signals in telecommunications cables to a higher level than ever. Category 6 is a performance classification for twisted pair cables, connectors and systems which is specified up to 250 MHz.
In many installations, in particular office buildings and the like, telecommunications cables are installed behind walls or in the plenum ceiling and floor spaces. These cables are typically terminated at a first end in a patch bay close to servers or other networking equipment and terminated at a second end at a receptacle in proximity to the user. At both ends the individual wires emerging from the end of the cable are spliced into the back of an appropriate connector with the front side of the connector being exposed to provide easy access for the insertion and removal of patch cables. In order to test the installed cables to assess whether or not they meet the specifications as dictated by the applicable standards, a testing equipment is attached to the front of the connector located at the patch bay and the front of the connector located at the receptacle. Measurement of the performance of length of cable, therefore, includes not only the length of cable but also the connectors through which access to the cable is gained.
As higher transmission frequencies give rise to complex changes in the behaviour of the various components, not only the performance of the individual components, in this case the cable and the two connectors, is important but also the manner in which these components are interconnected. A number considerations should be taken into account when installing telecommunications cables in order to ensure that they will meet the requisite testing specifications following installation. In particular, the cable termination on the back of the connector is an important factor and the conduction of an installation in a casual manner can lead to a significant degradation of performance.
One important electrical characteristic by which the performance of a telecommunications cable is measured is Near-End-Crosstalk, or NEXT. As is well known in the art, crosstalk is the undesired coupling from signal carrying wire to a collocated signal carrying wire. Crosstalk gives rise to undesirable interference which can severely affect transmission performance. For its part, NEXT is a measurement of crosstalk between two wire pairs of wires and is measured as the difference in signal strength between the interfering pair and the interfered pair. NEXT is directly affected by the manner in which the cable is terminated, and arises when the wires of two pairs are crossed. Crossing of wires can arise due to a number of reasons including failure to take appropriate care during installation or physical forces brought to bear on the cable or connector, for example during the installation of other cables.
Additionally, failure to take appropriate care when stripping the jacket from the length of cable as well as untwisting the twisted pairs can create a loop which can also affect performance. Therefore, installation of the cable on the back of each connector becomes very sensitive to the manner in which the installation is carried out by the installer.